CANNABIS IS A GATEWAY DRUG TO COCAINE (in adolescent male rats)

adolescent male rats walk around their cages more when given cocaine, if they had been given a cannabinoid drug the week before. but adult male rats didn't. some brain areas were affected too. nothing here about humans.  

original article: Scherma et al., 2020 (Proceedings of the National Academy of Sciences of the United States of America), reported in: The Daily Mail by Johnathan Chadwick on 20th April 2020 image source

this story was in episode 0 #rat #cannabis #cocaine #gateway #prefrontal

the error bar says

The Daily Mail this week screamed that cannabis really does lead users on to harder drugs like cocaine.

the reported study gave rats a synthetic cannabinoid drug twice a day for 11 days, with the dosage doubling every 4 days. a control group of rats instead had only a salt water drug under the same conditions.

one week after their last dose, all rats were injected with cocaine. the rats that had been on the cannabinoid drug were found to be more active – about 20-30 minutes after the cocaine, they walked around more than the control rats. this difference was about 10 extra metres walking over a 10 minute period – that's quite a lot for a rat.

in the rats' brains, lots of different chemicals were looked at, and some of those showed a strong statistical relationship between the brain areas examined and the drug combinations that the animals had received. the prefrontal cortex, which is an important part of the brain, was highlighted in particular.

is cannabis really a gateway drug to cocaine?

first, this is in rats. adolescent rats. adolescent, male rats. it didn't work in adult male rats, just 40 days older.

second, it's a single, synthetic cannabinoid drug, not cannabis. cannabis has several thousand different chemical constituents. this study tells us nothing about cannabis.

third, this was a one-way relationship – cocaine did not have the same effect on rats' responses to the cannabinoid. by The Daily Mail's logic, cocaine is therefore NOT a gateway drug to cannabis. so, is it OK for adolescent boys to inject cocaine? the error bar says no.

fourth, there is a LOT of detail in this paper – far too much to wade through, and way out of the error bar's expertise. it's not clear how much of these detailed results were theory-driven, and how much were post-hoc interpretations of a mass of data.

fifth, there is quite a strong whiff of cherry-picking of results. while the results in the main paper are rather strong, statistically speaking, several analyses in the appendices, which the main paper clearly relies upon, are much weaker. more problematically, several statistical interactions – a particular kind of statistical relationship – were reported as not significant in the results, but they were interpreted as if they were significant. misinterpreting statistical interactions is a common scientific error.


one synthetic cannabinoid drug affects young male rats' brains and behaviour in some ways, but adult male rats were not affected. how this relates to human drug use is unknown.


The Daily Mail: fudge - scientific story distorted